1. Technical Field
The present invention relates to a gas generating device, and particularly to an inflator for inflating an air bag to protect an occupant of a vehicle.
2. Description of the Prior Art
It is well known to protect a vehicle occupant by using an air bag that is inflated when the vehicle encounters sudden deceleration, such as in a collision. The air bag restrains movement of the vehicle occupant during the collision. The air bag is typically inflated by gas generated by activation of gas generating material. The gas generating material is contained in an air bag inflator.
The gas generated by the gas generating material is commonly passed through one or more filters before it enters the air bag. The filters remove combustion products and particulate matter from the gas, and also cool the gas. It is known to include one filter, along with the gas generating material, in a separate metal container within the inflator. The filter is commonly and henceforth referred to as a prefilter. The current state of the art prefilter is typically made from a strip cut from a sheet of woven wire mesh cloth. The strip is formed into an annular ring. The annular ring shape of the wire mesh is maintained by welding the strip at one or more overlapping regions of the wire mesh, or by forming the ring within a propellant chamber which maintains the annular ring shape of the wire mesh. To prevent the welded annular prefilter from rattling in the canister, the welded annular prefilter is formed into an oval shape. The oval shaped prefilter radially contacts the propellant canister side wall, thus preventing the woven wire mesh welded prefilter from rattling.